1. Field of the Invention
The present invention relates to an image forming apparatus controlling transition to a power-saving mode.
2. Description of the Related Art
Conventionally, power control for reducing power consumption has been done such that if an image forming apparatus is not used for a prescribed time period, transition to a low-power-consumption mode is made in which power supply to part of the apparatus is stopped. In the low-power-consumption mode, if a user operation is received through an operation panel of the apparatus, the low-power-consumption mode is cancelled and transition to a normal mode takes place. Such a transition is made possible by constantly scanning a touch panel or keys on the operation panel using a detection circuit arranged in the operation panel to detect a user operation. Recently, however, in order to further reduce power consumption in the low-power-consumption mode, power supply to the detection circuit is also stopped. In this case, the low-power-consumption mode cannot be cancelled by the user operation through the operation panel. Therefore, a method of cancelling the power-saving mode based on a detection result of a separately provided human body detection sensor has been proposed.
By way of example, Japanese Laid-Open Patent Publication No. 2006-251194 proposes a method in which a mat switch is provided on the floor in front of an image forming apparatus, and when a user coming to and standing in front of the apparatus is detected, the power-saving mode is cancelled.
According to the technique disclosed in Japanese Laid-Open Patent Publication No. 2006-251194, however, though it is possible to cancel the power-saving mode depending on whether a user is standing in front of the image forming apparatus, it is impossible to determine whether the user operates the apparatus or not. A method of providing a human body detection sensor near the operation panel may be possible. In that case, however, if detection distance is long, a person simply passing in front of the apparatus may be erroneously detected. If the detection distance is short, detectable range becomes narrow, so that detection of a user operation with respect to the entire surface of operation area possibly fails. By arranging a plurality of directional detection sensors over the entire surface of operation panel, it becomes possible to detect any operation on the entire surface of the operation area. This approach, however, leads to increased cost and excessively large operation panel.